WO2019092164A2

WO2019092164A2 - Device and method for determining the impedance on a tooth

Info

Publication number: WO2019092164A2
Application number: PCT/EP2018/080717
Authority: WO
Inventors: Michael Gente; Matthias WILLAMOWSKI
Original assignee: Philipps-Universität Marburg
Priority date: 2017-11-10
Filing date: 2018-11-09
Publication date: 2019-05-16
Also published as: DE102017126496A1; US20210169363A1; JP2021502188A; JP7028970B2; KR20200087195A; EP3706627A2; CN111565635A; WO2019092164A3

Abstract

The invention relates to a device and to a method and a device for determining the impedance (alternating current resistance) on a tooth. The impedance is determined by measuring the voltage at a given current intensity or by measuring the current intensity at a given voltage. The determination of the impedance on a tooth is used for diagnosing dental caries.

Description

DEVICE AND METHOD FOR DETERMINING IMPEDANCE TO

A TOOTH

The present invention relates to an apparatus and a method for determining the impedance of a tooth. The impedance of a tooth can be used for the diagnosis of dental caries (caries, carious lesion, carious lesions, plural: caries).

The caries is a dental disease in which the hard tooth tissue, so the enamel (Enamelum) and / or the dentin (dentin) are damaged. The dental hard tissue is also referred to as hard substance or tooth hard substance. Descaling, discoloration, cavitation (broken down tooth tissue) and lesions all the way to the pulp (pulp) are symptoms of tooth decay.

If the caries only affects the enamel, then it is spoken of a carious caries, the caries also affects the dentin, then talked of a dental caries. If caries affects the occlusal surface of a tooth, it is referred to as an occlusal caries, caries refers to the surfaces of a tooth adjacent to the neighboring teeth, then a proximal caries is used.

Since an untreated tooth decay leads to the loss of the affected tooth, it is essential to diagnose a tooth decay as early as possible. At the same time false positive results should be avoided as far as possible in caries diagnosis in order to rule out over-treatment. Caries diagnostics therefore strive for the highest possible specificity and sensitivity in order to be able to adequately care for the patient.

The diagnosis of caries on the tooth can be difficult, as small carious lesions can not visually distinguish them from discoloration of the enamel in the clinical examination. There are therefore the following two risks: On the one hand, the risk of over-treatment, if a discolored spot is incorrectly diagnosed as caries and is therefore drilled and filled, on the other hand, the risk of under-treatment, if a caries is not recognized and therefore remains untreated. The reliable diagnosis or the safe exclusion of a caries on the approximal surfaces of the teeth, ie those tooth surfaces that are attached to the border adjacent teeth. Between the approximal surfaces of two adjacent teeth is the interdental space, which can be individually very narrow. The narrower the interdental space, the worse the respective proximal surfaces are accessible to a visual examination. Especially with very narrow interdental spaces proximal caries are very easily overlooked.

State of the art

The following devices or procedures are used for the diagnosis of caries:

Visual diagnosis: The cleaned and dried tooth is examined for discoloration and cavitation (break-in of the dental hard tissue) by observation with the aid of a dental mirror under good illumination.

Tactile sounding: The cleaned and dried tooth is scanned with a dental probe.

Fiber optic transillumination (FOTI, diaphanoscopy, fiber optic transillumination): The hard tissue is examined with a cold light probe. The different light refraction behavior of healthy and carious diseased dental hard tissue is exploited. Carious substance becomes recognizable as a dark shadow due to a loss of light intensity. This is a good way to diagnose a dental caries.

X-ray examination: The X-ray examination with conventional or digital technique is carried out by means of bite wings (BF wings). In particular, enamel caries on proximal surfaces, ie the tooth surfaces on which the teeth of a row of teeth touch, can be well diagnosed.

Laser-assisted caries diagnostics (laser fluorescence measurement): The light from a laser fluorescence device with a wavelength of 650 nm is absorbed by both organic and inorganic substances. The laser fluorescence devices consist of at least one light source and one optic, which have a type-typical size. Since a carious lesion in the hard tooth substance is excited by the laser used to fluoresce, it can be concluded from the presence of fluorescence on a caries. This method is particularly suitable for the diagnosis of occlusal caries. Determination of the AC resistance at the tooth (impedance measurement):

In this procedure, the impedance of the hard tooth substance is determined with a suitable measuring device. In a caries, the electrical conductivity is significantly increased compared to a healthy hard tooth substance and thus significantly reduced the impedance. Since the enamel has a much higher impedance than the dentin, with this method, especially carious lesions of the enamel can be diagnosed. If a tooth decay has not yet led to cavitation and can therefore be detected neither visually nor by tactile probing, then the impedance measurement is a very suitable method.

For the determination of the impedance devices are used which work with alternating current. These measuring devices comprise at least one reference electrode, a measuring electrode and a measuring unit. The reference electrode is placed anywhere in the oral cavity. With the measuring electrode of the tooth to be examined is scanned. As soon as a carious change is touched with the measuring electrode, the impedance decreases. This change in impedance is registered by the measuring unit and displayed to the examiner, for example by an audible warning or visual indication. As an optical display, the pointer of an AC electrical resistance meter can be used or a light display that changes the color, for example, from green to red with the change in electrical resistance. The light indicator can be, for example, a LED scale with different colored diodes.

When scanning the surface of the tooth to be examined with the measuring electrode, especially the occlusal surfaces with their fissures and small pits are examined. If the measuring electrode touches a carious site, then the impedance is lowered because the enamel layer of the tooth is porous at carious sites. The disadvantages of the prior art are as follows:

Visual diagnosis: The interdental spaces and thus the approximal surfaces of a tooth are not or only very poorly accessible to the visual diagnosis. An approximal caries is thus often overlooked in visual diagnostics. The significance of this clinical examination method depends very much on the experience and color perception of the dentist. Physiological discoloration of the tooth can be misdiagnosed as caries.

Tactile sounding: If clumsy, tactile probing can lead to the onset of poorly mineralized enamel or other damage to the tooth. In addition, it provides only insignificantly more insight compared to the visual diagnosis. For these reasons, tactile sounding has become obsolete.

Fiber optic transillumination: Physiological tooth staining that can occur independently of caries falsifies the results of fiber optic transillumination, resulting in false positive diagnoses.

X-ray examination: Each X-ray examination represents a radiation exposure, which should always be kept as low as possible. There must therefore be a justifying indication for an X-ray examination, especially in children and pregnant women. Since the patient is not allowed to move in the least while making an X-ray, X-rays are often impractical in smaller children or those with limited cognitive function. Dental caries can easily be overlooked in X-ray examinations, as changes can only be diagnosed as carious when demineralization is already well advanced into the dentin. Occlusal caries can only be detected on an X-ray if the carious lesions are already deep enough to reach the dentin. Since the X-rays are absorbed and scattered by already existing fillings, caries directly under or in addition to an existing filling in the X-ray examination can not always be detected. Laser-assisted caries diagnostics: With this procedure, proximal caries can hardly be diagnosed because the laser fluorescence devices used can not be placed between two teeth (ie towards the approximal surfaces) due to their typical size. Physiological tooth staining, which can occur independently of caries, falsify the results of laser-based caries diagnosis. The laser fluorescence devices are expensive to buy and operate.

Determination of the AC resistance at the tooth (impedance measurement):

The composition and amount of saliva on the tooth to be examined and in the oral cavity affect the electrical conductivity and thus the impedance. If there is a lot of saliva on the tooth to be examined, then the impedance decreases, even if there is no decay. False positive findings are thus obtained, since in this case the electric current flows not only through the tooth but also through the saliva film on the tooth surface to the oral cavity, so there is often an unidentified electrical shunt. Likewise, the different levels of individual saliva in the patient may affect the impedance.

This disadvantage exists in particular in the measuring devices currently used for impedance measurement. The measuring devices currently used for impedance measurement have poor reproducibility of the measurement results, which can confuse the dentist. The problem is especially with repeated measurements during follow-up checks.

Since caries is most likely to develop in fissures and small pits of the tooth surface, carious changes beginning with oversized measuring electrodes can not be reliably detected.

The measuring devices currently used for impedance measurement have rod-shaped, cylindrical or wire-shaped measuring electrodes. Due to this type of electrode, the prior art measuring electrodes are not suitable for scanning the approximal surfaces of teeth. Thus, proximal caries can not be diagnosed with the currently known measuring devices. task

The present invention is intended to provide a device and a method with which the determination of the impedance of a tooth for the diagnosis of caries is improved. In particular, the influence of saliva present in the oral cavity should be reduced. In addition, the reproducibility of the measurements during follow-up should be improved in order to reduce confusion of the dentist and thus misdiagnosis. In addition, the diagnosis of caries in fissures and small pits of the tooth surface should be improved in order to reliably detect even early stages of tooth decay. In addition, the diagnosis of a proximal caries with suitable measuring electrodes should be made possible.

Solution of the task

The object of the invention is achieved by claim 1 (device) and claim 14 (method). In particular, the object according to the invention is achieved by the following developments with regard to the prior art:

- Use of an insulating gel 9 with a specific electrical resistance of p> 500 Ω ^■ m to avoid the disturbing influence of saliva.

- Improvement of the measuring electrode 5 by coupling with a compensating electrode 6: As a result, the current, the side of the

Measuring electrode 5 would drain over the tooth surface, passed over the compensating electrode 6. The compensating electrode 6 functions as a shield for the measuring electrode 5.

- Adjustment of the measuring electronics in the measuring unit 2: The execution of the AC measurement with the lock-in technology will be stable

Measured values achieved even at very low currents. This enables stable measured values to be achieved for currents between 10 nA and 2 μΑ.

- Carrying out the measurement according to the principle of carrier frequency measurement technology. - The measuring unit 2 provides a defined sinusoidal voltage by means of a function generator. Preferably, this sine voltage has a frequency of 600 Hz and an average voltage of about 70 mV Urms. This voltage is applied via an isolation amplifier both to the measuring electrode 5 and to the compensating electrode 6.

The device 1 according to the invention and the method according to the invention thus determine the impedance of the tooth hard substance to be examined in an improved manner. In the case of caries, the impedance at the affected area of the hard tooth substance decreases. To determine the impedance Ohm's law is applied. The impedance is determined by a calculation from the measured values of the current flow between the measuring electrode 5 and the reference electrode 4 at a predetermined voltage. Alternatively, the impedance can also be determined by a calculation from the measured values of the voltage at a given current flow between the measuring electrode 5 and the reference electrode 4.

In order to reduce the influence of the saliva present in the oral cavity, the present saliva is first eliminated in the determination of the impedance of the tooth to be examined, and then an insulating gel 9 is applied. This insulating gel 9 may have only a low electrical conductivity and must be non-toxic and inexpensive to manufacture. Preferably, the insulating gel 9 has a resistivity of p> 500 Ω-m. The viscosity of the insulating gel 9 should be so high that it adheres to the tooth to be examined. It is advantageous if, for better recognition, it has a color that differs from all other structures in the oral cavity. Thus, it can be easily determined by visual inspection whether the insulating gel 9 has been applied in sufficient quantity and at the intended locations. Particularly advantageous for the insulating gel 9, a gel-like preparation of 0.9 g of the galactose polymer agar (or agar-agar) to 100 ml of distilled water (distilled water.) + 1 ml of dye has been found. The dye used is advantageously a blue food color such as, for example, anthocyanins (E 163), brilliant blue FCF (E 133), indigotin (E 132) or patent blue V (E 131).

Alternatively, the insulating gel 9 can also be prepared from gelatin or starch. In one embodiment, the insulating gel 9 is in the form of flexible bags or pads which can be pressed onto the tooth to be examined and conform to the tooth surface. These bags or pads have the advantage that they can be stored better and if necessary can be removed from a single package.

The device 1 according to the invention has at least the following further components:

A measuring unit 2: The measuring unit 2 comprises at least one function generator, an isolating amplifier, a lock-in amplifier, a voltage indicator, an evaluation unit and an output device for an acoustic, optical and / or haptic signal. The measuring unit 2 is connectable to the reference electrode 4, the measuring electrode 5 and the compensating electrode 6. Advantageously, this connection is a plug-in connection, so that the electrodes 4, 5 and 6 can be cleaned after a patient's use and reused.

The measuring unit 2 provides via the function generator, the AC voltages available, which are applied to the electrodes 4, 5 and 6, with which the measuring unit is connected. The measuring unit 2 measures the current flowing from the measuring electrode 5 through the tooth to the reference electrode 4. From the resulting current, the evaluation unit of the measuring unit 2 determines the height of the impedance for a given voltage. In an alternative embodiment, the measuring unit 2 measures the voltage at a given current intensity. In any case, the evaluation unit of the measuring unit 2 detects the height and the change of the impedance at at least two different positions of the tooth to be examined.

Thus, the evaluation unit of the measuring unit 2 registers a change in the impedance, processes and evaluates the measurement results and provides the examiner with suitable feedback via the output means, for example an acoustic warning signal and / or a visual display and / or a haptic display. The output means of the measuring unit 2 can be connected to the measuring unit 2. The currents measured to determine the impedance of a tooth are very small. In order to evaluate this better, a lock-in amplifier is used. This avoids interference at low measuring currents. Thanks to the lock-in amplifier and the resulting lock-in technology, stable readings are achieved even at very low currents in the range from 10 nA to 2 μΑ.

A handle 3: The handle 3 is designed such that the device 1 with the measuring unit 2 can be held during the examination and the electrodes 4, 5 and 6 of the device 1 can be placed in the oral cavity or on the tooth to be examined. The handle 3 has a surface made of an electrically insulating material, for example plastic such as polycarbonate or polyethylene.

In the handle 3, the measuring unit 2 can be integrated, so that the handle 3 and the measuring unit 2 only need a common housing. In this advantageous embodiment, the handle 3 is designed so that the advantageous plug-in connections of the electrodes 4, 5 and 6 are made possible with the measuring unit 2.

A reference electrode 4: It consists of an electrically conductive material and is placed anywhere in the oral cavity. It is connected to the measuring unit 2 via an electrical conductor. In a preferred embodiment, the reference electrode 4 is formed connectable to the measuring unit 2 via a plug. Thereby, the reference electrode 4 can be easily changed after use in a patient. The reference electrode 4 is designed so that it can be easily cleaned and sterilized.

A measuring electrode 5: It consists of an electrically conductive material. It is connected to the measuring unit 2 via an electrical conductor. In a preferred embodiment, the measuring electrode 5 is formed connectable to the measuring unit 2 via a plug. Thereby, the measuring electrode 5 can be easily changed after use in a patient. The measuring electrode 5 is designed so that it can be easily cleaned and sterilized.

The measuring electrode 5 is arranged relative to the reference electrode 4 such that an alternating current can flow between the measuring electrode 5 in a first position on a tooth to be examined and the reference electrode 4. With the measuring electrode 5, the surface of the tooth to be examined is scanned. Thus, the measuring electrode 5 is spent in at least one further position on a tooth to be examined. At the point where the measuring electrode

5 touches the tooth, it displaces together with the compensation electrode 6, the insulating gel 9 from the tooth surface and the circuit is over the

Reference electrode 4 closed. If this site of the tooth is not carious, then the impedance is very high because the intact enamel and intact dental bone have a high electrical resistance of over 600 kΩ. As soon as the measuring electrode 5 touches the area of the carious change, the impedance drops below 480 kQ. This change in impedance is determined by measuring unit 2 via the measurement of current flow, processed, evaluated and output to the examiner.

An equalizing electrode 6: It consists of an electrically conductive material. It is connected to the measuring unit 2 via an electrical conductor. In a preferred embodiment, the compensation electrode 6 is formed connectable to the measuring unit 2 via a plug. This allows the compensation electrode

6 after use in a patient easily be changed. The compensation electrode 6 is designed so that it can be easily cleaned and sterilized. The compensating electrode 6 is at the same electrical potential as the measuring electrode 5. Thus, it has the same electrical potential as the measuring electrode 5. The compensating electrode 6 is structurally coupled to the measuring electrode 5. It serves to shield the measuring electrode 5.

The measuring electrode 5 and the compensating electrode 6 are not electrically connected to each other, but separated by an insulating layer 7 (insulating layer, insulator). Between the measuring electrode 5 and the compensating electrode 6 so an insulation layer 7 is attached.

This structural arrangement of the mechanical coupling with simultaneous electrical insulation ensures that the insulating gel 9, which surrounds the measuring electrode 5 and the compensating electrode 6, the same electrical potential as at the measuring electrode 5. This ensures that flows over the Tooth surface flow, exclusively from the Compensating electrode 6 and not from the measuring electrode 5. The compensating electrode 6 thus causes the tooth enamel at the point to be examined on the tooth and the applied insulating gel 9 have the same electrical potential as the measuring electrode 5. This prevents the generation of an electric field which generates a current flow from the measuring electrode 5 via the tooth surface to the oral cavity and thus to the reference electrode 4. Since this unwanted current flow reduces the reproducibility and the accuracy of the impedance determinations, it is essential to prevent this. An insulating layer 7: The insulating layer 7 is disposed between the measuring electrode 5 and the compensating electrode 6 in the form that these two electrodes are electrically insulated from each other and no current can flow between these two electrodes. The insulating layer 7 is made of a suitable insulating material such as plastic, for example polycarbonate or polyethylene. The insulation layer 7 thus prevents, together with the insulating gel 9, that currents which flow over the tooth surface originate from the measuring electrode 5. This significantly improves the reproducibility and accuracy of the measurements.

A schematic representation of the device according to the invention are shown in FIGS. 1 and 2.

The method according to the invention comprises the following steps:

The tooth to be examined is dried as far as possible with methods known from the prior art in order to prevent the individually different influences of the saliva. For draining, the saliva film may be expelled from the tooth, for example with an air blower. After drying, for example, cotton rolls or a rubber dam keep new saliva away.

- The tooth to be examined is wetted with the insulating gel 9 according to the invention. This tooth is so wetted, for example, with a gel-like preparation of 0.9 g of agar-agar to 100 ml of distilled water (distilled water.) + 1 ml of dye. The wetting takes place over the entire visible surface of the tooth or even only at the sites to be examined.

- This creates standardized and comparable measurement conditions. In particular, the access of the natural, electrically highly conductive saliva is prevented, which interferes with the measurement of the current flow and thus the determination of the impedance as a shunt to the oral cavity and thus to the reference electrode 4.

The reference electrode 4 is placed anywhere in the oral cavity without coming into direct contact with the measuring electrode 5 and the compensating electrode 6. This site must not show any pathological changes (eg inflammation, ulcers or tumorous changes). This site is not treated prior to the application of the reference electrode 4 and is thus saliva wet. Since the electrical resistance of the tissue between the tooth to be examined and the reference electrode 4 is negligibly small compared to the electrical resistance of the tooth hard substance, the spatial distance between the reference electrode 4 and the examined tooth is negligible. Therefore, it is irrelevant at which point of the oral cavity the reference electrode 4 is placed.

- The measuring electrode 5 is applied to the site of the tooth to be examined and brought into contact with this. With the measuring electrode 5 so the surface of the tooth to be examined is scanned. At the point of contact with the tooth, the measuring electrode 5 displaces the insulating gel 9, which thus forms a wall-like, insulating layer around the measuring electrode 5.

- Due to the mechanical coupling of the compensating electrode 6 to the measuring electrode 5, the compensating electrode 6 is applied simultaneously to the point of the tooth to be examined and the insulating gel 9 forms a wall-like, insulating layer around the compensating electrode 6 around. The measuring electrode 5 and the compensating electrode 6 so to speak dip into the insulating gel 9 and thus come into contact with the tooth surface. Thus, the circuit between the measuring electrode 5 and the reference electrode 4 is closed.

- Between the measuring electrode 5 and the reference electrode 4, an alternating electrical voltage U is applied. This AC voltage U points For example, a frequency of 600 to 2000 Hz. Preferably, its maximum amplitude is about 200 mV. Preferably, its mean amplitude Urms is about 70 mV.

- To the compensating electrode 6, an AC voltage is also applied, which in their amplitude, their frequency and their phase position of the

Voltage at the measuring electrode 5 corresponds.

- The measuring unit 2 now measures the current flowing through the measuring electrode 5 at a constant voltage flowing through the tooth to the reference electrode 4. This current flow is used as a measured value, from which the measuring unit 2 determines the impedance. Small currents correspond to a large impedance, large currents correspond to a small impedance.

Alternatively, the measuring unit 2 measures the voltage applied to the measuring electrode 5 at a constant current intensity. This voltage is used as the measured value, from which the measuring unit 2 determines the impedance.

The determination of the impedance Z is based on Ohm's law Z = U / I.

The inventive arrangement of the compensating electrode 6 and the use of the insulating gel 9 according to the invention causes the current flow from the measuring electrode 5 can only lead into the tooth to be examined via the tip of the measuring electrode 5 and not laterally over the tooth surface to the gingiva (gums) and thus into the oral cavity to the reference electrode 4. So it disturbing electric fields and unwanted current flows are prevented. This achieves much better reproducibility and accuracy, allowing for precise follow-up examinations. Likewise, this achieves a significantly improved specificity and sensitivity compared with the impedance determination in the prior art.

Further embodiments

In one embodiment, the reference electrode 4 is designed as a bent, stainless wire. In one embodiment, the reference electrode 4 is made of a metal such as titanium, silver or iron, or of a metal alloy, or preferably of stainless steel, in another embodiment, the reference electrode 4 is made of carbon.

In one embodiment, the measuring electrode 5 is made of a metal such as titanium, silver or iron, or of a metal alloy, or preferably of stainless steel, in another embodiment, the measuring electrode 5 is made of carbon.

Advantageously, an alternating voltage with a frequency of about 600 Hz and a maximum amplitude of about 200 mV is applied to the measuring electrode 5. Thus, the mean amplitude Urms is about 70 mV. In one embodiment, the compensating electrode 6 is made of a metal such as titanium, silver or iron, or of a metal alloy, or preferably of stainless steel, in another embodiment, the compensating electrode 6 is made of carbon.

In one embodiment, the measuring electrode 5 is resiliently mounted to compensate for the irregularities of the tooth surface (fissures, small pits).

In a preferred embodiment, the measuring electrode 5 is formed as an elongate electrode with a tapered tapered end. This allows measurements to be carried out even in the smallest recesses of the tooth surface. Likewise, measurements on very small carious suspected changes in fissures or small pits of the tooth surface can be performed. Measuring electrodes 5, whose diameters are smaller than 1.5 mm, have proven particularly suitable for this purpose.

In one embodiment, the measuring electrode 5 and the compensation electrode 6 mechanically coupled thereto are formed as a sheet-like foil. Thus, measurements can also be carried out in the interdental spaces on the approximal surfaces of the tooth to be examined. As a carrier material for the film, a plastic or other substance can be used, which has a very low electrical conductivity, such as polycarbonate or polyethylene. Thus, in this embodiment, this carrier material acts as an insulating layer 7. The carrier material for the film is preferably transparent, so that the dental staff can recognize the tooth surface through the film. In this carrier material (ie the insulating layer 7), the measuring electrode 5 and the compensating electrode 6 are incorporated. In this case, the measuring electrode 5 and the compensating electrode 6 are made of an abrasion-resistant material, for example of a metal such as titanium, silver or iron, or of a metal alloy or preferably of stainless steel, or of carbon.

In one embodiment, the measuring electrode 5 formed as a sheet-like film and the compensation electrode 6 mechanically coupled to it have a reinforced edge. This facilitates the placement of the measuring electrode 5 and compensating electrode 6 between two teeth (that is to say in the intermediate tooth area) formed as a flat foil. Likewise, the crumpling of the measuring electrode 5 and compensating electrode 6 formed as a flat film is thereby prevented.

In one embodiment, the reinforced edge of the sheet is formed as a compensating electrode 6. In another embodiment, the reinforced edge of the sheet is formed as a measuring electrode 5. In one embodiment, the sheet-like film has two measuring electrodes 5 and two compensating electrodes 6, which can be controlled separately by the measuring unit 2. As a result, after the placement of the sheet in the space between two adjacent teeth, only one tooth with the first measuring electrode 5 and the first compensating electrode 6 can be examined and then the other tooth with the second measuring electrode 5 and the second compensating electrode 6 Advantage that when examining the Approximalflächen two adjacent teeth, the foil must be placed only once in the interdental region. This is particularly advantageous in narrow interdental areas for the patient and the dentist.

In one embodiment, the compensating electrode 6 is formed as a cylindrical tube, in another embodiment as a cylindrically wound wire. In both embodiments, the compensating electrode 6 encloses the centrally arranged measuring electrode 5 and both are electrically isolated from each other by an insulating layer 7. In a further embodiment, the compensating electrode 6 is arranged opposite the measuring electrode 5 such that they are axially displaceable relative to one another. This is achieved for example by the incorporation of a resilient element 8 in the measuring electrode 5 or the compensating electrode 6. Advantageously, the externally arranged compensation electrode 6 is coupled via a spring 8 with the centrally arranged measuring electrode 5. It is essential that these two electrodes are electrically isolated from each other by an insulating layer 7. By this arrangement, the following advantage is achieved: If one presses the measuring electrode 5 in a fissure or a small pit of the tooth to be examined (ie where caries preferably arises), the tip of the compensating electrode 6 follows the tip of the measuring electrode 5 and both electrodes attach themselves tightly to the tooth surface. As a result, incorrect measurements and measurement fluctuations are reduced.

In one embodiment, the electrodes 4, 5 and 6 are designed as disposable electrodes. In this case, the electrodes 4, 5 and 6 are advantageously connected via a plug connection with the measuring unit 2.

In a preferred embodiment, the measuring unit 2 is integrated in the handle 3, so that the handle 3 and the measuring unit 2 only need a common housing.

Figure legend Figure 1 shows a schematic representation of the device 1 according to the invention in a longitudinal section: The measuring unit 2 and the handle 3 are arranged independently of each other. The measuring electrode 5 and the compensating electrode 6 are coupled to each other and placed on the tooth to be examined (shown schematically). The compensating electrode 6 is tubular (cylindrical) at the point of contact with the tooth and thus shields the measuring electrode 5. The reference electrode 4 is placed anywhere in the oral cavity. The insulating gel 9 is not yet applied to the surface of the tooth.

Figure 2 shows a schematic representation of the device 1 according to the invention in a longitudinal section: The measuring unit 2 is integrated in the handle 3, so that only a common housing is needed. The measuring electrode 5 and the compensating electrode 6 are coupled to one another and to the tooth to be examined (shown schematically) placed. The compensating electrode 6 is tubular (cylindrical) at the point of contact with the tooth and thus shields the measuring electrode 5. The reference electrode 4 is placed anywhere in the oral cavity. The insulating gel 9 is applied over the entire surface of the tooth to be examined. At the contact point of the measuring and the compensating electrode 5 and 6 with the tooth they displace the insulating gel 9. Thus, the insulating gel 9 forms a wall-like border around the measuring and the compensating electrode 5 and 6 around.

Figure 3 shows a schematic representation of the device 1 according to the invention in a longitudinal section: The measuring unit 2 is integrated in the handle 3, so that only a common housing is needed. The measuring electrode 5 and the compensating electrode 6 are coupled to each other and placed on the tooth to be examined (shown schematically). The compensation electrode 6 is formed at the contact point to the tooth as a cylindrically wound wire and thus shields the measuring electrode 5 from. The reference electrode 4 is placed anywhere in the oral cavity. The insulating gel 9 is not yet applied to the surface of the tooth.

Figure 4 shows a schematic representation of the device 1 according to the invention in a longitudinal section: The measuring unit 2 is integrated in the handle 3, so that only a common housing is needed. The measuring electrode 5 and the compensating electrode 6 are coupled to each other and placed on the tooth to be examined (shown schematically). The measuring electrode 5 is spring-mounted with a resilient element 8. As a result, the measuring electrode 5 is arranged to be axially displaceable with respect to the compensating electrode 6. As a resilient element 8, a spring is provided. If one presses the measuring electrode 5 in a fissure or a small pit of the tooth to be examined (ie where caries preferably arises), the tip of the compensating electrode 6 follows the tip of the measuring electrode 5 and both electrodes are close to the tooth surface. The compensation electrode 6 is formed at the contact point to the tooth as a cylindrically wound wire and thus shields the measuring electrode 5 from. The reference electrode 4 is placed anywhere in the oral cavity. The insulating gel 9 is not yet applied to the surface of the tooth. Figure 5 shows a schematic representation of the device 1 according to the invention in a longitudinal section: The measuring unit 2 is integrated in the handle 3, so that only a common housing is needed. The measuring electrode 5 and the compensating electrode 6 are coupled to each other and placed on the tooth to be examined (shown schematically the right tooth). The measuring electrode 5 and the compensating electrode 6 are formed as a flat foil and can thus be placed in the interdental space to examine the approximal surfaces of the right tooth. The reference electrode 4 is placed anywhere in the oral cavity. The insulating gel 9 is not yet applied to the surface of the tooth.

FIG. 6 shows an exemplary embodiment of a schematic representation of the measuring electrode 5 and of the compensating electrode 6, which are formed as a flat foil. The sheet-like film simultaneously represents the insulation layer 7. The measuring electrode 5 is designed as a planar, in this embodiment rectangular electrode. The compensating electrode 6 is embedded as a wire-shaped electrode in the sheet-like film. The compensating electrode 6 is arranged around the rectangular measuring electrode 5 so as to shield the measuring electrode 5.

FIG. 7 shows an exemplary embodiment of a schematic representation of the measuring electrode 5 and of the compensating electrode 6, which are designed as a flat foil. Both the measuring electrode 5 and the compensating electrode 6 are embedded as straight, wire-shaped electrodes in the sheet-like film. The flat film simultaneously represents the insulation layer 7.

FIG. 8 shows an exemplary embodiment of a schematic representation of the measuring electrode 5 and of the compensating electrode 6, which are designed as a flat foil. The sheet-like film simultaneously represents the insulating layer 7. The measuring electrode 5 is designed as a flat, in this embodiment, round electrode. The compensating electrode 6 is embedded as a wire-shaped electrode in the sheet-like film. The compensating electrode 6 is arranged around the circular measuring electrode 5 so as to shield the measuring electrode 5. As an exemplary embodiment, FIG. 9 shows a cross-section through a schematic representation of the measuring electrode 5 and of the compensating electrode 6, which are designed as a sheet-like foil. The sheet-like film simultaneously provides the insulation layer 7 On the two opposite surfaces of the film are each a measuring electrode 5 and a compensating electrode 6 as straight running, wire-shaped electrodes embedded in the sheet-like film. By suitable programming of the measuring unit 2, either the measuring electrode 5 and the compensating electrode 6 of one side are activated and used for one measurement, or the measuring electrode 5 and the compensating electrode 6 of the other side. As a result, two adjacent teeth can be examined with a flat film without having to change the film.

List of reference signs Inventive device

measuring unit

Handle

reference electrode

measuring electrode

compensation electrode

insulation layer

resilient element for mechanical coupling of the compensating electrode 6 to the measuring electrode 5, for example a spring insulating gel

Claims

claims

1 . Device (1) for determining the impedance of a tooth, comprising

a measuring unit (2) for generating an alternating voltage,

a reference electrode (4) connected to the measuring unit (2),

a measuring electrode (5) connected to the measuring unit (2),

a compensating electrode (6) connected to the measuring unit (2), wherein the measuring electrode (5) and the reference electrode (4) are arranged relative to each other such that between the measuring electrode (5) and the reference electrode (4) in a first position on a to be examined tooth can flow an alternating current;

and wherein the measuring unit (2) can determine the impedance from the resulting current intensity;

and wherein the measuring electrode (5) and the compensating electrode (6) are at the same electric potential;

and wherein between the measuring electrode (5) and the compensating electrode (6) an insulating layer (7) is mounted to isolate the two electrodes from each other;

and wherein the measuring unit (2) comprises an evaluation unit which detects the change of the impedance in a determination at at least two positions of the tooth to be examined;

and wherein the measuring unit (2) is provided with an output means for outputting the

Impedance and / or the impedance change is connectable;

and wherein the device (1) comprises a handle (3) for holding the

Measuring unit (2) during the determination, so that the device (1) can be placed during the determination on the tooth to be examined,

characterized in that the device (1) comprises an insulating gel (9) arranged so that the measuring electrode (5) is isolated from saliva in the oral cavity.

2. Device (1) for determining the impedance to a tooth according to claim 1, characterized in that the insulating gel (9) has a specific electrical resistance of p> 500 Ω-m.

Device (1) for determining the impedance to a tooth according to claim 2, characterized in that the insulating gel (9) comprises agar and distilled water.

4. Device (1) for determining the impedance to a tooth according to claim 1 or 2, characterized in that the insulating gel (9) contains a dye, preferably a blue dye.

5. Device (1) for determining the impedance to a tooth according to one of the preceding claims, characterized in that the output means of the measuring unit (2) comprises an optical and / or acoustic and / or haptic display.

6. Device (1) for determining the impedance to a tooth according to one of the preceding claims, characterized in that the reference electrode (4), the measuring electrode (5) and / or the compensating electrode (6) made of a metal such as titanium, silver or Iron, or consist of a metal alloy, or preferably made of stainless steel or carbon.

7. Device (1) for determining the impedance to a tooth according to one of the preceding claims, characterized in that the measuring electrode (5) and the compensating electrode (6) are formed as a sheet-like film.

8. Device (1) for determining the impedance of a tooth according to one of the preceding claims, characterized in that the insulating layer (7) consists of plastic such as polycarbonate or polyethylene.

9. Device (1) for determining the impedance of a tooth according to one of the preceding claims, characterized in that the handle (3) has a surface made of an electrically insulating material, for example plastic such as polycarbonate or polyethylene.

10. Device (1) for determining the impedance to a tooth according to one of the preceding claims, characterized in that the measuring electrode (5) with a resilient element (8) is resiliently mounted and thereby against the compensating electrode (6) is arranged axially displaceable ,

1 1. Device (1) for determining the impedance of a tooth according to one of the preceding claims, characterized in that the measuring electrode (5) has a tapering end.

12. An apparatus (1) for determining the impedance of a tooth according to one of the preceding claims, characterized in that the reference electrode (4) is designed as a bent, stainless wire.

13. Device (1) for determining the impedance to a tooth according to one of the preceding claims, characterized in that the measuring unit (2) in the handle (3) is integrated, so that only a common housing is needed.

14. A method for determining the impedance of a tooth with a device (1) according to one of the preceding claims, comprising the steps:

1 . Eliminate the saliva on the tooth to be examined

2. Attach the insulating gel (9) to the tooth to be examined

3. Positioning the measuring electrode (5) in a first position on the tooth to be examined, wherein the measuring electrode (5) meets directly on the tooth

4. Position the reference electrode (4) anywhere in the oral cavity

5. Applying an alternating voltage between the measuring electrode (5) and the reference electrode (4) with the measuring unit (2)

6. Measuring the resulting current

7. Determination of the impedance from the AC voltage and the resulting current

8. repeating steps 3 to 7 at at least one further position of the tooth to be examined

9. Comparison of the at least two impedances, wherein it is detected whether the impedance changes.

15. Use of a device (1) according to one of claims 1 to 13 for determining the impedance to a tooth.